After Hurricane Ida, satellites track Gulf of Mexico oil spills4 min read . Updated: 16 Sep 2021, 05:51 PM IST
- NOAA’s analysis of the view from space helps frame recovery and containment methods to address environmental hazards
While energy companies have struggled to restore output since Hurricane Ida tore through the Gulf of Mexico, satellite surveillance of oil spills left in the storm’s wake has continued around the clock, documenting the potential environmental impact.
The Coast Guard, which is responsible for investigating oil spills and other pollution in the aftermath of the storm, has been busy following up on leads. As of Tuesday, it had responded to more than 2,200 reports of pollution in the region since the Category 4 hurricane struck in late August. That number was up from about 1,500 last week.
Much of the information that response teams rely on when investigating and containing oil spills in the open water originates in space. The National Oceanic and Atmospheric Administration’s satellite division continuously monitors marine pollution year-round.
When the unit identifies a possible spill, it notifies partner agencies and the public, providing information about the area of the spill, the thickness of the oil and, when it can, the suspected source, which it derives from satellite data and the presence of existing pipelines and platforms in the area.
NOAA began making its marine-pollution reports available to the public in March 2018. The number and size of suspected spills in the Gulf declined in the 12 months after pandemic lockdowns took effect in early 2020, when global demand for oil fell. Detection has risen this summer, and particularly since Hurricane Ida struck.
More reports don’t necessarily mean there were more spills. The satellite detections are published as unconfirmed spills, and NOAA assigns a level of confidence to each report. In some cases, the agency might issue multiple reports for a single, continuing spill.
There is also a seasonal factor in satellite surveillance. When analyzing visible imagery, experts have an easier time seeing oil pollution from space in the summer because the angle of the sun is more favorable.
“When the sun illuminates an oil sheen, the analyst is able to observe a white, shimmery appearance against a dark ocean background. Therefore during late spring through early fall, there is a higher likelihood of detecting oil in satellite imagery," said Ellen Ramirez, a supervisory scientist at NOAA’s Satellite Analysis Branch.
“In the winter season, a dark oil sheen can easily blend into the dark ocean background," she said.
Color in visible imagery helps analysts distinguish between oil and possible other features, such as vegetation. It also gives them an idea of areas within a possible spill where oil concentration is thick or thin. That information is critical to response teams in determining what recovery and containment methods to use.
“Oil-spill responders that are going out into the open water often have to deploy very expensive resources such as vessels or aircraft in order to direct their cleanup and mitigation strategies. They want to know where the areas of oil are thin versus relatively thick, so they can determine how to clean it up," Ms. Ramirez said.
NOAA’s satellite analysis primarily relies on two types of data to detect marine oil. If visible imagery isn’t available when a satellite makes a pass over a given area—either because it happens to be at night or the surface is obscured by cloud cover—radar data can provide analysts with clues about where oil is present in water.
A radar transmits pulses of energy from the satellite down to the surface, and then a portion of that energy bounces back to the satellite. The amount of return in these pulses of energy depends on the smoothness or roughness of the surface they reflect off. Oil flattens the surface of water, which lessens the return and results in a darker shade in a radar-generated image.
In 2010, NOAA’s space-based oil-spill surveillance program was still in an experimental phase, but played a critical role in the response to the Deepwater Horizon disaster, a rig explosion that killed 11 people and resulted in the worst offshore oil spill in U.S. history. Since then, the program has expanded its role beyond disaster response to monitor for oil spills in U.S. waters on a 24/7 basis.
“Over the years, as we continued to analyze new satellite data that’s collected over the ocean, we started to notice numerous smaller spills from oil-production facilities, drilling units, potential spills from pipeline networks and even from shipwrecks," Ms. Ramirez said. “There are dozens of shipwrecks in U.S. waters that have a lot of oil onboard that pose a significant environmental threat."
Pollution can also occur naturally in the form of oil seeping up through the seafloor. And not all oil pollution is accidental.
Over the past decade, in addition to reporting on smaller spills, the program began identifying suspected intentional oil discharges, in which ships illegally release waste into the water rather than spending the time and money required to dispose of the waste legally.
“If we observe an anomaly that is uncharacteristic of a ship wake, we generate a possible pollution report and inform the U.S. Coast Guard," Ms. Ramirez said.
This story has been published from a wire agency feed without modifications to the text
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